Originally Posted by ctdrftna
Winona van Norman machine, it's easier to hold like that, I use shim stock to square the deck
Yes it is quick and easy to set off the oil pan rails, and if the block was machined correctly to begin with then you are fine, but most block decks are not machined parallel to the oil pan rails.
Did you check your piston to deck clearance at tear down?
If your block had a .003 tilt from front to rear, with your set up you cut that tilt back in it.
Now if you look at the attached pics, you see #1 cyl is .016 on the hole and #4 is .025 in the hole, so I am showing a diffrence of .009
When I had the block set up in my machine, I found .006 tilt on the block, and was able to mill to correct this tilt.
Now about the other .003, during the factory maching all the parts have a tolerance, so part of the remaing .003 can be in the ground stroke of the crank, in the center to center of the con rod, the maching of the crown of the piston or in the wrist pin location of the piston.
But I know I have the same distance from the main centerline to the deck surface now.